1. Field of Invention
The present invention relates to a method of injection molding of polyethylene terephthalate resin which has prominent moldability by using a platinum wire which has a good resistance to oxidation and considerable temperature difference of the platinum wire, enabling to produce a coil heating wire with a slender diameter.
2. Description of the Prior Art
In general, polyethylene terephthalate resin, hereinafter referred to as "PET resin", is used as a raw material for injection molding such as various types of medical bottles or containers, preforms for decanter bottles (Cold-Parison) and the like.
More particularly,
(1) a bottle made from the PET resin is transparent, of good gloss and appearance, and easy to coloring; PA1 (2) the weight of the bottle is one seventh to one tenth compared with the same capacity of a glass bottle, and the mechanical strength of the bottle is strong enough so that the bottle does not break even if it falls to the ground; PA1 (3) the bottle has good barrier property to gas permeability against oxygen, carbon dioxide or other gases, thereby enabling to preserve effectively a substance of contents; PA1 (4) the bottle is odorless, of excellent property to maintain fragrance, and less adsorbent to flavor; PA1 (5) molecules of PET resin are composed only of carbon, hydrogen and oxygen, therefore poisonous gases have not generated at incineration; PA1 (6) combustion energy is comparatively small, i.e. 5,500 kal/kg, as almost same as timber, thus, the bottle shall not damage a incinerator; PA1 (7) the bottle has outstanding chemical resistance to any acid and/or other solvents only excluding strong bases and some of special bath liquids; and, PA1 (8) the bottle meets the Japanese standards based on the Food Sanitation Act and also meets the standards and regulations of Food and Drug Administration in U.S.A., thereby the bottle has eminent food hygienic property.
Thus, the PET resin and its products like a medical bottle or container has various significant features and versatile uses.
FIG. 5 and FIG. 6 show the main portions of an apparatus of injection molding of the PET resin in the prior art; where 1 is a runner part, 2 is a sub-runner part, 3 is a gate, and 4 shows cavity respectively.
This cavity 4 is provided with the shape to form the preform for a beverage bottle (Cold-Parison) as shown in FIG. 7.
Also shown in FIG. 5, a conical probe 5a which penetrates through a runner part 1 in a longitudinal direction, is provided with a body heater 6 thereby heating the runner part 1, and in FIG. 6, a conical probe 5b is provided with the body heater in a longitudinal direction to be included in and to heat a runner part 1.
Based on these constructions as described hereinabove, in the case when the body heater 6 is operated to inject the PET resin in molten conditions under a desired injection pressure, the PET resin is injected from the runner part 1 through the sub-runner part 2 and the gate 3 into the cavity 4, and as shown in FIG. 7, Cold-Parison a having a sprue sub-runner part a 1 is produced.
And as the sprue sub-runner a 1 is whitened partly, this whitened part is to be cut along the c--c cut line at the next step.
As stated hereinabove, while the moldings of the PET resin by the method of injection molding in the prior art is transparent in the normal operation, there is a problem of whitening phenomenon of moldings that a bit of solid and not molten resin near the gate (gate land) flows through the line during the molding process, so that the whitened resin is produced as the sprue sub-runner.
Thus, in general, the processing of PET resin by the direct gate method is one of the most difficult methods of injection molding among the crystalline resins, and the moldings of PET resin does not satisfy the desirable and required functions, especially its mechanical strength due to whitening phenomenon of moldings. Therefore, in general, the direct gate method is usually not adopted to manufacture the medical tubes or containers, such as blood-collecting tubes and others, also the preform for beverage bottles (Cold-Parison) both of which are used to be utilized in many fields; however, even in a few cases when this method should be adopted for manufacturing of PET injection molding, it is unavoidable to have a shape provided with a sprue sub-runner (cutting after molding; ref. FIG.7) which should adsorb whitening, and as the result this method shall require ineffective consumption of a raw material, inferior quality (whitening dispersion) and need a cutting process, and furthermore, the medical container shall be manufactured in clean rooms, therefore the diffusion or scattering of resin residues must be avoided at the cutting process.